In this protocol, volunteers are recruited to undergo a two hour cytapheresis procedure for collection of large quantities of human circulating white blood cell components (lymphocytes or monocytes) from single donors for the use of National Institute on Aging laboratory investigators. Pheresis packs are supplied to individual qualified investigators as anonymous packs for use in basic studies of lymphocyte and monocyte function and studies of immune function in the aging process. Based on extensive modified American Bloodbank Association questionaires, laboratory screening including assessment of complete blood counts, urinalysis, liver and renal function as well as virologic screening including HIV and Hepatitis testing, the possibility of influence of extraneous infections or other chronic medical conditions on laboratory studies is minimized. In the course of the last year, the established donor pool has remained constant at approximately 70 participants with 221 procedures performed. Cell packs were supplied to individual investigators for research purposes. Based on trends over the last several years, there is an increasing need for cells by a range of laboratories with expectation for continued expansion of participants as well as procedures in this protocol in the next year.